Some aspects of the pharmacology of diphenyleneiodonium, a bivalent iodine compound.

1. Previous studies have established that diphenyleneiodonium binds to and inhibits the respiratory enzyme NADH dehydrogenase and also catalyses an exchange of Cl- for OH- across membranes. 2. The hypoglycaemia produced by diphenyleneiodonium was confirmed and shown to be reversible at a dose of 4 mg/kg in starved rats. 3. The lethality of diphenyleneiodonium in mice was cumulative. 4. Presumably as a result of the Cl-/OH- exchange, diphenyleneiodonium-treated rats excreted less Cl- than controls in the first 12 h after administration. However, the swelling of erythrocytes observed in vitro did not occur in vivo. 5. When [125I]diphenyleneiodonium was administered to rats and rabbits, its distribution did not appear to be governed by its binding to NADH dehydrogenase. Reasons for this are discussed. 6 Over 90% of the radioactivity excreted in the faeces of rabbits could not be extracted with boiling water or with dil. HNO3.